The present invention relates to web supporting and drying apparatus. In drying a moving web of material, such as paper, film or other sheet or planar material, it is often desirable that the web be contactless supported during the drying operation, in order to avoid damage to the web itself or to any ink or coating on the web surface or surfaces. A conventional arrangement for contactlessly supporting and drying a moving web includes upper and lower sets of air bars extending along a substantially horizontal stretch of the web. Heated air issuing from the air bars floatingly supports the web in a substantially sinusoidal path and expedites web drying. The air bar array is typically inside a dryer housing which can be maintained at a slightly sub-atmospheric pressure by an exhaust blower that draws off the volatiles emanating from the web as a result of the drying of the ink or coating thereon.
U.S. Pat. No. 3,739,491 discloses a high velocity air flotation dryer for drying a running web along the lines of the foregoing. A plurality of spaced air nozzles are positioned on opposite sides of the web. Heated air issuing from the impingement nozzles impinges on the running web to floatingly support and dry the web. The nozzles are in air-receiving communication with an air supply fan through suitable ducting. A burner is located in the ducting downstream from the supply fan outlet for heating the supply air which flows through the air nozzles and impinges on the web. The burner employed is a blow-through type, in that it is located on the outlet or pressure side of the supply air fan. As a result, in order to supply combustion air to the burner, a fan or blower which has a higher pressure output than the supply air fan is required, which can be expensive.
In conventional designs where a draw-through style burner is used, a duct or large plenum collects the return air, and the burner fires into that duct or plenum to heat the air. The duct or plenum is in communication with the inlet of the supply air fan, and supplies the thus heated return air to the fan. Such an arrangement necessarily sends all of the return air past the burner, and is not efficient.
It is therefore an object of the present invention to reduce dryer cost by eliminating ducting otherwise necessary for burner operation. Reduced ductwork also decreases the supply fan pressure requirement which reduces motor size and energy usage.
It is a further object of the present invention to provide a draw-through style burner which fires directly into the dryer enclosure.
It is a still further object of the present invention to regulate the amount of air subjected to the burner flame.